Don't checkout Homebrew/brew master for non-developers

[Bo98]

Currently we check out master when cloning Homebrew/brew:

install/install.sh

Line 933 in 3d2b88b

execute "${USABLE_GIT}" "reset" "--hard" "origin/master"

brew update will correct this to be on a stable tag, but picking master initially is not ideal because it means brew update will perform a downgrade and we don't test downgrades (but will accept fixes where there are issues). An example of an issue caused by a downgrade is #825.

Instead, short of a full stable-branch setup that brew update does, an initial detached tag checkout would be much better. Detached tag checkouts without a stable branch now work without downgrades since Homebrew/brew@2a02038.

[MikeMcQuaid]

Agreed, thanks @Bo98!

[MikeMcQuaid]

Fixed by #839